Sulfur gases, and particles are common air pollutents. The measurement of air-borne particulate sulfur provides important data in air pollution monitoring and control. The common methods for measuring air-borne sulfur particulates are based on collections of sulfur particles on filters or impactors followed by chemical analysis of the resulting samples. Analysis techniques include: gravimetric analysis based on conversion to BaSO.sub.4, Ba(C10.sub.4) titrimetry, infrared attenuated total reflectance spectroscopy, ion chromatography, X-ray fluorescence spectroscopy, and X-ray photoelectron spectroscopy. All of these techniques depend on collections of samples followed by subsequent laboratory analysis. These methods utilize considerable periods of time and do not provide for continuous measurements of air-borne particles.
A semi-continuous sulfuric acid aerosol monitor has been developed. This monitor uses the same instrument to sample and make an analysis of the sampling. The monitor operates by collecting samples on Teflon filters and then volatilizing them into a dry N.sub.2 stream flowing to a flame photometric detector. The sampling times are in the 15 to 30 minute range. The sulfur particles samples are collected on surfaces which are generally exposed to ambient sulfur gases. The possibility of conversion of some of the gaseous sulfur to particle form on these surfaces will produce erroneous results. Any collection surface subjected to atmospheric aerosols would become contaminated, and its collection and subsequent characteristics will change with time.
Methods which do not depend on collecting of particles on surfaces have been developed. A humidified nephelometer has been used to identify sulfuric acid aerosols. A temperature programmed heater at the inlet to a nephelometer has also been used to identify sulfuric acid aerosols. Both of these methods have analysis times of a few minutes.
Another technique to continuously monitor the sulfur aerosol uses a flame photometric monitor. A sulfur gas scrubber at the inlet to the monitor allows only sulfur particles to enter the flame. The particle concentration is directly measured. The output signal level of this instrument is barely above the flame background noise. In order to improve the signal to noise ratio, the sulfur particle must be integrated for several minutes. A filter is switched to the line for several minutes to obtain an integrated average background signal. The difference between the average non-filtered signal and the signal with the filter in line gives the signal component due to the sulfur particles. The total analysis time is approximately five minutes.